Classical canonical transformation theory as a tool to describe multidimensional tunnelling in reactive scattering. Hopping method revisited and collinear H+H2 exchange reaction near the classical threshold

Abstract

Classical canonical perturbation theory is applied in the vicinity of the saddle point for a chemical reaction. This is done by applying successive canonical transformations in the scope of the Gustavson–Birkhoff approach. It is shown that the calculated approximate classical integrals of motion can be used to describe classically forbidden tunnelling processes. They are also organically embedded into a hopping method to incorporate tunnelling effects into classical trajectory simulations of chemical reactions. The applicability of the proposed scheme is demonstrated for the collinear H+H₂ exchange reaction using the double many-body expansion potential energy surface.